A dense connective tissue layer about 0.2mm thick enveloping the roots of teeth, located between the cementum and alveolar bone and consisting mainly of collagen fibres (desmodontium) and ground substance (proteoglycans and glycoproteins). The cell types considered to be part of the periodontal ligament are the fibroblast, cementoblast, osteoblast, and osteoclast. It contains blood vessels, lymph vessels, and nerves. The periodontal ligament forms from collagen fibres within the dental follicle (Hertwig's sheath); cellular remnants of Hertwig's sheath remain between the collagen fibres into adult life. Its functions are to provide a support mechanism for the tooth, to maintain the vertical position of the tooth, to form, maintain, and repair the surrounding alveolar bone and cementum, to detect pressures on the tooth through proprioceptive sensors, and to provide nutrients to the cement-forming cells (cementoblasts). The fibres of the periodontal ligament are grouped together to provide tooth stability. With age, the width of the periodontal ligament decreases and there is a decrease in collagen and protein synthesis.
Berkovitz B. K. B. Periodontal ligament: structural and clinical correlates. Dent Update 2004;31:46–54.